polish: add additional test

note that filtering is still required for synchronous error bubbling with stream.

With defer, patches are not executed if the initial field set execution fails, but with stream, the initial items (perhaps of zero length) will execute and will create the stream record.

Author: yaacovCR

src/execution/__tests__/stream-test.ts

@@ -979,6 +979,39 @@ describe('Execute: stream directive', () => {
       },
     });
   });
+  it('Filters payloads that are nulled by a later synchronous error', async () => {
+    const document = parse(`
+      query { 
+        nestedObject {
+          nestedFriendList @stream(initialCount: 0) {
+            name
+          }
+          nonNullScalarField
+        }
+      }
+    `);
+    const result = await complete(document, {
+      nestedObject: {
+        async *nestedFriendList() {
+          yield await Promise.resolve(friends[0]);
+        },
+        nonNullScalarField: () => null,
+      },
+    });
+    expectJSON(result).toDeepEqual({
+      errors: [
+        {
+          message:
+            'Cannot return null for non-nullable field NestedObject.nonNullScalarField.',
+          locations: [{ line: 7, column: 11 }],
+          path: ['nestedObject', 'nonNullScalarField'],
+        },
+      ],
+      data: {
+        nestedObject: null,
+      },
+    });
+  });
   it('Does not filter payloads when null error is in a different path', async () => {
     const document = parse(`
       query {